Throttle issue...?

[live4theking]

68 NYer 440 factory Holley 4160 List 3918

I put a renew kit in the carb a few days ago. The car idles fine and pulls about 16# of vaccum. It seems to be running fine down the road as long as I drive gently. If I do a WOT burst for a few seconds when I pull off it won't come all the way back to idle. It's probably a few hundred rpm above idle. Even if I blip the throttle or rev it in neutral it won't come back down all the way.

I pulled it in the garage and removed the air cleaner with it still running and the throttle looked to be in the idle position, against the adjusting screw. When I shut it down it dieseled momentarily. There isn't any fuel spray out the tail pipe so it doesn't seem to be running rich.

When I fired it up just a minute or two later it idled fine again.

Anyone else ever run into something like this?

 

[FURYGT]

Floats sticking?

 

[commando1]

Anyone else ever run into something like this?

Yes.
Holleys on an Edelbrock manifold (if you have one) have an interference where the choke lever hits the unused choke pot. Needs to be notched. Check that.

 

[Newport 66]

Do you have a vacuum leak?

 

[live4theking]

Floats sticking?

I checked it once, but if I don't find something else I suppose I'll be checking them again.

Yes.
Holleys on an Edelbrock manifold (if you have one) have an interference where the choke lever hits the unused choke pot. Needs to be notched. Check that.

Stock intake, stock carb - so hopefully this isn't the issue.

Do you have a vacuum leak?

Possibly, I checked the other night, but I'll probably end up checking again tonight.

One of the guys at work suggested checking the diaphragm for the secondaries might not be fully closing. So, I'll be trying to look at this tonight too.

 

[Davea Lux]

When you check the diaphragm, be sure the spring is properly seated and that the secondary butterfly is not getting interference from the carb base gasket. Sounds like your secondary butterfly is sticking open, lucky you, usually they just stuck shut!

Dave

 

[live4theking]

Dave,
I sure hope you're right. That would be a quick fix.

 

[live4theking]

CND is the results of tonight's testing, could not duplicate.
First I manually moved the throttle to WOT and manually actuated the secondaries to check for binding several times. They always seemed to close fine.
Second i started it and took it for a gentle warm up run.
Third hooked vacuum gauge to the port for the choke pull off 16#. Fastened the gauge down and off for a ride. I did five WOT sprints it only seemed to hang up a little bit from the first one.
Not sure if manually running the secondaries freed something up or what.

 

[65sporty]

I was thinking the secondaries were sticking open some, but if you couldn't duplicate.... More testing is required, take it out and drive it more, a lot more

 

[70bigblockdodge]

There is a linkage piece that ensures secondaries close when throttle is released. It rides in a slot on secondary side, it may be hanging the primary open a touch or not adjusted to ensure secondary closure.
Check to see it's not binding and holds against end of slot when at curb idle.
It may have just gotten a little wonky when you had it off /apart.

 

[CBODY67]

What about the throttle return springs? There is a spring on the carb's linkage, but it takes the two auxiliary springs to make everything work correctly.

There might be enough wear on the primary throttle shafts to let them not be "square" when they close, but that would take a lot of wear to do that. A little "slack" is normal.

CBODY67

 

[live4theking]

I was thinking the secondaries were sticking open some, but if you couldn't duplicate.... More testing is required, take it out and drive it more, a lot more

I agree I would've driven it to work today, but they are calling for storms.

There is a linkage piece that ensures secondaries close when throttle is released. It rides in a slot on secondary side, it may be hanging the primary open a touch or not adjusted to ensure secondary closure.
Check to see it's not binding and holds against end of slot when at curb idle.
It may have just gotten a little wonky when you had it off /apart.

I'm familiar with the slotted piece that you're referring to. I'll give that a good looking over. I'm hoping that something was just a little wonky to use your term.

 

[live4theking]

What about the throttle return springs? There is a spring on the carb's linkage, but it takes the two auxiliary springs to make everything work correctly.

There might be enough wear on the primary throttle shafts to let them not be "square" when they close, but that would take a lot of wear to do that. A little "slack" is normal.

CBODY67

All springs are in place.

 

[CBODY67]

With all springs in place and operational, might be a situation where the carb cleaner soak removed some "lubricating" residual fuel deposits on the throttle shaft and bores? Perhaps some fuel-resistant spray lube might put some non-sticky lubricity back into the throttle shaft bores? Providing there are no other "bindings" in the linkages?

Just a thought,
CBODY67

 

[live4theking]

With all springs in place and operational, might be a situation where the carb cleaner soak removed some "lubricating" residual fuel deposits on the throttle shaft and bores? Perhaps some fuel-resistant spray lube might put some non-sticky lubricity back into the throttle shaft bores? Providing there are no other "bindings" in the linkages?

Just a thought,
CBODY67

I don't know if this was the best choice or not, but a put a little bit of graphite on the shafts. Maybe that got worked in the other night.

The forecast isn't great, but I intend to take it out some this afternoon to do some running.